This application makes reference to, incorporates the same herein, and claims all benefits accruing under 35 U.S.C. xc2xa7119 from an application entitled Shadow Mask Frame Assembly for the Flat CRT earlier filed in the Korean Industrial Property Office on 10 Dec. 1999, and there duly assigned Ser. No. 99-56747 by that Office.
1. Field of the Invention
The present invention relates to a flat CRT (cathode ray tube), and more particularly, to a shadow mask of a flat CRT.
2. Description of the Background Art
A color CRT includes a shadow mask frame assembly which is installed in a panel where a fluorescent film is formed and a funnel coupled to the panel forming a seal. The funnel includes a neck portion in which an electron gun is inserted and a cone portion around which a deflection yoke is installed. In the color CRT having the above structure, an electron beam emitted from the electron gun passes through an electron beam passing hole of a shadow mask and lands on a fluorescent substance of a surface of a screen of the panel, forming an image.
A surface of a screen of a typical color CRT is designed to have a predetermined curvature considering the trace of the electron beam emitted from the electron gun. The shadow mask is designed to have a curvature corresponding to that of the surface of the screen. However, the curved shadow mask bulges toward the panel by being heated by the electron beam emitted from the electron gun, which is referred to as a doming phenomenon. The doming phenomenon prevents the electron beam from accurately landing on a fluorescent surface.
A flat CRT has recently been developed to provide a flat screen. Since the panel of the flat CRT is flat, the shadow mask installed in the CRT should be flat. In order to realize flatness, a tension force is applied to the shadow mask of the flat CRT.
A shadow mask frame assembly includes a frame having two support members installed parallel to each other and two elastic members, either end portion of each of which is secured at each of the support members, and a flat shadow mask having an edge portion that is welded to the support members. In the shadow mask, a plurality of strips are connected by a plurality of bridges.
In the shadow mask frame assembly, since the flat shadow mask is supported in the state of receiving a great tension force provided by the elastic members through the support members, the flat shadow mask receives a Poisson contraction. During the operation of a CRT, thermions emitted from the electron gun partially pass through slots of the shadow mask while the remaining thermions collide against the strips and the bridges to heat and expand the shadow mask. The amount of deformation due to the thermal expansion increases from the center of the shadow mask to the periphery of the shadow mask due to the bridges.
Accordingly, the shadow mask is deformed due to a combination of the Poisson contraction and thermal expansion. Furthermore, as the bridges uniformly formed at the front surface of the shadow mask interferes with deformation of the strips, an unbalanced tension force is generated at each portion of the shadow mask and the amount of deformation at each portion is different. In particular, deformation occurs greater at the central portion between both ends in a horizontal direction. Such deformation of the shadow mask prevents the thermions emitted from the electron gun from accurately landing on the fluorescent film. Therefore, the color purity of a displayed image is lowered.
Exemplars of the art are U.S. Pat. No. 5,355,049 issued to Sung for ASSEMBLY OF SHADOW MASK FRAME WITH INNER SHIELD FOR COLOR CATHODE RAY TUBE, U.S. Pat. No. 5,898,259 issued to Reyal for SHADOW MASK FRAME OF A CATHODE RAY TUBE, ITS PROCESS OF MANUFACTURE, AND SUSPENSION ELEMENT OF A SHADOW MASK FRAME, U.S. Pat. No. 4,678,963 issued to Fonda for SHADOW MASK FOR A COLORED IMAGE TUBE AND IMAGE TUBE COMPRISING THE SAME, U.S. Pat. No. 5,877,586 issued to Aibara for SLOT-TYPE SHADOW MASK, U.S. Pat. No. 5,030,880 issued to An for SHADOW MASK FOR COLOR CATHODE RAY TUBE, U.S. Pat. No. 3,652,895 issued to Tsuneta et al. for SHADOW-MASK HAVING GRADUATED RECTANGULAR APERTURES, U.S. Pat. No. 5,856,725 issued to Ueda for SHADOW MASK WITH EDGE SLOTS CONFIGURATION, U.S. Pat. No. 4,168,450 issued to Yamauchi et al. for SLOT TYPE SHADOW MASK, U.S. Pat. No. 4,300,069 issued to Nolan for COLOR PICTURE TUBE HAVING IMPROVED SLIT TYPE SHADOW MASK AND METHOD OF MAKING SAME, U.S. Pat. No. 4,973,283 issued to Alder et al. for METHOD OF MANUFACTURING A TIED SLIT MASK CRT, U.S. Pat. No. 4,942,332 issued to Alder et al. for TIED SLIT MASK FOR CATHODE RAY TUBES, U.S. Pat. No. 5,523,647 issued to Kawamura et al. for COLOR CATHODE RAY TUBE HAVING IMPROVED SLOT TYPE SHADOW MASK, U.S. Pat. No. 6,057,640 issued to Aibara for SHADOW MASK FOR COLOR CATHODE RAY TUBE WITH SLOTS SIZED TO IMPROVE MECHANICAL STRENGTH AND BRIGHTNESS, U.S. Pat. No. 6,140,754 issued to Ko for STRUCTURE OF SHADOW MASK FOR FLAT CATHODE RAY TUBE, U.S. Pat. No. 4,794,299 issued to Chiodi et al. for FLAT TENSION MASK COLOR CRT FRONT ASSEMBLY WITH IMPROVED MASK FOR DEGROUPING ERROR COMPENSATION, and U.S. Pat. No. 4,915,658 issued to Lopata et al. for REFERENCE AND SUPPORT SYSTEM FOR FLAT CRT TENSION MASK. I have found that the background art does not show a shadow mask of a cathode ray tube that reduces Poisson contraction and is stable to external impacts.
It is therefore, an object of the present invention to provide a shadow mask of a flat cathode ray tube in which Poisson contraction thereof is reduced and is stable to external impacts.
It is another object to have a cathode ray tube that is stable and maintains a high picture clarity.
It is yet another object to have a cathode ray tube that reduces Poisson contraction within a shadow mask by forming a particular pattern within the shadow mask.
It is still yet another object to have a frame of a shadow mask of a display device that adds stability of the display device.
Accordingly, to achieve the above objects, there is provided a shadow mask frame assembly of a flat CRT having a shadow mask including a plurality of strips formed at a main body in a vertical direction by being separated a predetermined distance by slits and a plurality of bridges forming slots by connecting neighboring strips and sectioning the slits, in which the slots include a first slot group including slots having a wide interval between the bridges and a second slot group including slots having a narrow interval between the bridges, first and second support members secured at a long side portion of the shadow mask, and a frame including first and second elastic members, either end portion of each of which is secured to each of the first and second support members, for applying a tension force to the shadow mask.
It is preferred in the present invention that at least two second slot groups are formed at upper and lower portions of the shadow mask in a vertical direction while the first slot group is formed between the two second slot groups in the vertical direction. The first slot group is formed at the central portion of the main body in the vertical direction. The number of the slots forming the first slot group in the vertical direction is one. The number of the slots forming the second slot group in the vertical direction is at least three. The length of each of the slots forming the second slot group is substantially the same. The length of each of the second slot groups in the vertical direction and the length of the first slot group in the vertical direction are substantially the same. The length of the second slot group in the vertical direction is substantially the same as the length of the first slot group in the vertical direction.
To achieve another aspect of the above object, there is provided a shadow mask frame assembly of a flat CRT having a shadow mask including a plurality of strips formed at a main body in a vertical direction by being separated a predetermined distance by slits and a plurality of bridges forming slots by connecting neighboring strips and sectioning the slits, in which a portion where the bridges are formed and a portion where the bridges are not formed are alternately disposed in a horizontal direction, first and second support members secured at a long side portion of the shadow mask, and elastic members, either end portion of each of which is secured to each of the first and second support members, for applying a tension force to the shadow mask.
Also, it is preferred in the present invention that the intervals between the bridges in the vertical direction are substantially the same.